[ux][s]: improve ui and ux a bit.

 * select dropdowns are now nicely styled and layout is better
 * display full name of series / country in graph (requires saving the indicator and country code info)
[deps][xs]: bump jquery dep to 1.9.1 (would allow us to use typeahead etc).
[README][s]: add some doc about data sources.
[js][xs]: change config for data source to datahub.io rather than local.